A known on-board evaporative emission control system includes a vapor collection canister that collects fuel vapor emitted from a tank containing a volatile liquid fuel for the engine, and a canister purge solenoid (CPS) valve for periodically purging collected vapor to an intake manifold of the engine. The CPS valve in the known evaporative emission control system includes an electromagnetic solenoid that is under the control of a purge control signal generated by a microprocessor-based engine management system. The electromagnetic solenoid may be a digital on/off solenoid, or a proportional solenoid.
CPS valves that include a proportional solenoid are premium valves that use precision components to control the position of a flow restricting pintle. The position of the pintle is varied with the amount of current supplied to the solenoid. It is believed that known CPS valves that include a proportional solenoid have favorable response and control characteristics. However, known CPS valves that include a proportional solenoid suffer from a number of disadvantages, including high cost, as compared to valves having a lower parts count.
CPS valves that include a digital on/off solenoid have a low parts count and simple construction and are typically less costly than CPS valves that include a proportional solenoid. It is believed that known CPS valves that include a digital on/off solenoid have favorable response characteristics. However, known CPS valves that include a digital on/off solenoid suffer from a number of disadvantages, including poor control and high noise levels.
It is believed that there is a need for a CPS valve having the favorable response and control characteristics of a proportional solenoid valve, and the low manufacturing cost of a digital on/off solenoid valve.